Ok, here's the latest woe. I'm currently daily driving my truck. I sold my daily driver last week, and won't get around to picking up a new on until this weekend. I noticed on Friday that the truck was a little hard to start when I left work on Friday, and at stoplights it was idling pretty rough. Got home fine, and after the kids went to bed, I went out to have a look and see what was going on. I couldn't start it, with the symptoms of a dead battery (the battery is only 6 months old). I pulled the battery and put it on the charger over night. The next morning, I put the battery back in, and it fired right up. Ran some errands and it ran just fine. Saturday night, I went out to pick up some dinner, and while I was out, it started running rough at idle again, and had some stumbling while driving at low RPMs. After dinner, I went out to take another look, and the battery was dead again. I put it on the charger again, and Monday went to go troubleshoot again. With the truck in park, idling, the volt meter is dead between drain and charge. In drive, idling, it's just a bit towards the drain side. If I turn on the AC or headlights, it's definitely towards drain. If I rev it up in park or drive the needle moves to the charge side, and as soon as the revs drop off, it's back to drain. If I leave it idling in drive, particularly with the AC or lights on, it will eventually start stumbling badly (after 20-30 minutes). Revving the engine resolves it for a minute or two, then it's back to running like crap.

Can alternators get "weak" or do they just fail outright? How about the voltage regulator? It was replaced the week before I bought the truck, so is about 18 months old. Obviously a poor charge would eventually drain the battery, but will it cause it to run rough as described when the battery is low? The charger showed only about 25% charged the first time I hooked it up to the charger. is there an easy way to test the alternator and the voltage regulator, or should I just pull them off and take them to the parts store? Anyone know what the output of the stock alternator is? Can I get one with a higher output without causing any problems?

Thanks for the help, yet again

 

To check for the alternator charging....

Start the truck, and while its idling, use a screwdriver to touch the round piece on the back, if its charging, the little area (About the size of a silver dollar) will be magnetized...If not, the alt is not working...Whether its the alt or not...It won't show that.....

My charging system just crapped out....Turns out, it was a green/red wire that goes to the starter relay on the fender....

 

Is the ALT belt loose.

 

Jim, good call. I do have a squealing belt. Sounded like it's on the drivers side, and having recently replaced the AC compressor belt, I assumed it was the PS belt, but it could be the alternator belt I guess. The behavior wouldn't be out of line for a slipping belt.

 

A loose, or slipping alt belt can cause this type of issue, as well as a loose/weak connection on the alt or regulator.
The alt or regulator could be going out, but I'd check the belt and all connections first, then move towards having the alt output tested.
Do you have a volt meter? If so, see what the voltage is at the battery with the engine running, idle and revved up some. Any lower than ~13.5V when running, and the battery won't charge properly.

 

Thanks for the input. I'll check the belt when I get home and go from there.

 

Well, the Alt belt was definitely the one squealing, there was over an inch of play in the belt. I tightened it up, and it's quiet now, but that doesn't seem to have completely fixed the issue. With the AC and lights on, the meter is to the drain side. I couldn't find the multimeter last night to test while running. I'll try that tonight if I can find it. it also continues to run rough after a short drive.

 

As you are finding out, the factory ammeter is pretty useless in figuring out if the truck is charging or not. Find that voltmeter.

 

So useless, that dad installed a volt meter under the dash in his 74. Now there's no more "guessing" at what's going on.
I can't understand why Ford stuck with the useless alt guage for so long, when a volt meter would have been so much more handy......

 

Has anyone installed a volt meter in place of the ammeter? Yes, I know about the circuit board, that isn't too big an issue.